1. Field of the Invention
The present invention relates to non-destructive inspection of steam turbines. More specifically, the invention provides an apparatus for performing non-destructive inspection of steam turbine blades while the blades remain within the turbine.
2. Description of the Related Art
Steam turbines typically include a plurality of rows rotating blades, with each successive row having a slightly larger diameter than the preceding row. The individual blades within each row define end regions in close proximity to the end regions of the adjacent blades, having a Z-shaped gap in between. These end regions are typically referred to as the Z-shroud region. The last, largest diameter blades in the turbine, known as the L-0 blades, also include cylindrical stand-offs at the midpoints of the blades,.defining a narrow gap between the cylindrical standoffs of adjacent blades. The gap between adjacent blades at the Z-shroud and snubber regions may be about 0.15 inch. The blades make contact in these regions when a turbine is operating, due to bending and twisting of the blades, resulting in the potential for contact stresses and cracking within these regions. Additionally, the narrow gap between adjacent blades in these regions makes inspection of these regions difficult while the blades are within the turbine.
Although present turbine designs provide access to the region within the turbine behind the L-0 blade, the heat within a turbine makes it undesirable for individuals to remain in this region for extended periods of time even considering that the turbine will be off when entered. Inspection of the blades while they are in the turbine is desirable to minimize the time required for the inspection, and therefore the time during which the turbine may not be operated.
Accordingly, there is a need for a non-destructive testing apparatus for inspecting the Z-shroud and snubber regions of turbine blades without removing the blades from the turbine.
There is a further need for an apparatus permitting this inspection to be performed remotely, thereby limiting the amount of time during which an individual must be within the turbine.